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Advanced Automotive Gasoline Engines HIGHLIGHTS © IEA ETSAP - Technology Brief T01 – April 2010 - www.etsap.org Advanced Automotive Gasoline Engines HIGHLIGHTS PROCESS AND TECHNOLOGY STATUS – Internal combustion engine technology is constantly evolving. A number of improvements in gasoline-powered vehicles have been made to optimize combustion, improve fuel economy and reduce emissions. Examples of advanced gasoline technologies include reduced engine friction losses, direct gasoline injection, engine downsizing with turbocharger, variable valve actuation (VVA) and homogeneous charge compression ignition (HCCI). The majority of these technologies are already commercially available or close to being on the market. Although HCCI technology is still under development for both gasoline and diesel engines, it promises improvement in fuel economy and exceptionally low NOx and soot emissions. PERFORMANCE AND COSTS – A study by the US Environmental Protection Agency (EPA, 2008) presents the potential CO2 reduction and incremental compliance costs for a number of advanced gasoline technologies as compared to conventional port-fuelled injection vehicles. The costs account for both direct manufacturing costs and indirect costs. The technologies covered - and related CO2 reduction and incremental compliance costs in 2006 US dollars – include a) engine friction reduction (1-3%, $0-126); b) homogeneous direct injection (1-2% $122-525); c) stratified direct injection (9-14%, $872-1275); d) downsizing with turbocharging (6-9%, $120-690); e) variable valve timing (1-4%, $59-209); f) variable valve control (3-6%, $169-1262); and g) cylinder deactivation (6%, $203). POTENTIAL AND BARRIERS – Car ownership is expected to grow in many OECD countries as well as in emerging economies. Demanding environmental concerns and fuel economy standards, as well as increasing fuel prices, are the major drivers for advancement in engine technologies. The IEA study Energy Technology Perspectives (IEA, 2008) suggests that improving the fuel economy of light-duty vehicles (car, small van and sport utility vehicles) would be one of the most important and cost-effective measures to help reduce CO2 emissions in the transport sector. Given the maturity of some advanced gasoline technologies, and the near-term and cost-effective solutions they can offer to energy and emissions concerns, there is neither technical-economic nor infrastructure barrier for deployment, although some technical bottlenecks have to be solved for technologies such as the HCCI. ________________________________________________________________________________ TECHNOLOGY STATUS AND PERFORMANCE - Advanced gasoline technologies include a variety of Table 1 – Advanced Technologies for Gasoline Engines new components and systems aimed at optimizing combustion and thereby improving the fuel economy Technology Status and reducing the emissions of greenhouse gases and Reduced Engine Friction Losses Production other pollutants. Major innovations are listed in Table 1. Direct Gasoline Injection (incl. Production Reduced engine friction technologies include homogeneous/ stratified charge) systems, components and materials that minimize the Downsizing with Turbocharging Production friction between moving metal parts in the engine. Variable Valve Actuation Production These technologies are available in a significant Cylinder Deactivation Production number of engine designs [1]. Several friction reduction Variable Compression Ratio Prototype opportunities have been identified in piston surfaces Homogeneous charge compression ignition Prototype and rings, crankshaft design, improved material (HCCI) coatings and roller cam followers. Various studies suggest that the CO2 reduction potential for engine friction reduction technologies may range from 1-5% (stoichiometric) DI engines, a high-pressure fuel [1,2,3]. injector sprays fuel directly into the combustion chamber early enough in the cycle to promote In the gasoline direct injection (DI) engines, fuel is injected at high pressure directly into the combustion homogeneous fuel-air mixing. These engines have the chamber rather than into air intake manifolds. The key potential to reduce hydrocarbon emissions, increase advantage is the improvement in fuel efficiency. The power and improve fuel economy, while taking technology was developed more than 10 years ago and advantage of the highly-effective catalytic after- a number of different manufacturers are now using treatment systems, the same as the port fuel injection these types of engines in commercially available (PFI) engines. Various studies suggest a CO2 emission vehicles. The use of sulphur-free fuels is necessary to reduction potential ranging from 1-5% [1,3,4] in obtain the maximum benefit from this technology. comparison with PFI and multi-point injection. These engines are often supplemented with turbo-charging, Depending on the ignition and combustion mode and on 1 2 the formation process of the mixture, DI engines can be supercharging , or both . They are available from categorized in homogeneous charge, and stratified charge, spark ignition. In the homogeneous charge 1 Turbochargers and superchargers are air compressors that allow more air into an engine; turbochargers are powered by exhaust gases, while superchargers run directly on engine power. 1 Please send comments to [email protected], [email protected], [email protected], [email protected] (Authors), and to [email protected] and Giancarlo Tosato ([email protected]), Project Coordinators © IEA ETSAP - Technology Brief T01 – April 2010 - www.etsap.org several automobile companies worldwide, and more valve. The advantages of using VVT include deployment is expected in the near future. Stratified improvement in full-load volumetric efficiency which charge DI engines involve concentrating fuel spraying results in increased torque and reduction in pumping close to the spark plug rather than throughout the whole losses during low-load operation, which results in of the combustion chamber. The aim is to produce an reduced fuel consumption. Depending on the design, overall lean stratified mixture. These engines operate EPA (2008) estimates that VVT may enable 1-4% in at least two modes, depending on load and speed. reduction in CO2 emissions compared to fixed-valve During low-load and low-speed operation, the engine engines. The VVL system controls the lift height of the runs with a stratified charge and with lean mixtures. At valves using two different approaches: discrete VVL high-load and high-speed operation, the engine and continuous VVL. Compared to VVT, VVL offers a operates as a stoichiometric homogeneous charge DI further reduction in pumping losses and low-load fuel engine. These engines offer higher CO2 reduction consumption. There may also be a small reduction in potential than homogenous charge DI engines, ranging valve train friction when operating at low valve lift. Most from 8-14% compared to PFI and multi-point injection of the fuel economy gain is achieved with VVL on the [1, 2 , 3, 4], However, major impediments are cost, inlet valves only. This is considered to be a cost- complexity and the requirement of expensive lean NOx effective technology when applied in addition to VVT traps in the exhaust after-treatment system. Stratified (cam phase control) [1]. A number of manufacturers charge DI engines are currently in production (wall- have implemented VVL (or VVT with VVL) into their guided variant), but there is a shift towards the spray- fleet [10, 11, 12]. Based on standard (ECE) driving guided injection variants [1, 4, 5] as they improve cycles, automotive brochures suggest that the VVL injection precision and targeting towards the spark plug, system provides fuel savings of up to 10%, and thus increasing lean combustion stability. These improves cold start behaviour [10]. Various studies systems offer improved fuel economy and reduced confirm CO2 reductions of 3-7%. emissions. Stratified charge spray-guided DI engines 3 Cylinder deactivation allows an engine to run on are nearing production . The availability of low-sulphur part (usually half) of its cylinders during light-load fuels and improved lean catalyst technology will speed operation. For example, a 6-cylinder (V6) engine will the process up. run on all cylinders during acceleration (or under high Engine downsizing is seen as one of the most load), and switch to four or three cylinders for cruising important technologies to reduce fuel consumption and or low-speed drive. This technology is aimed at large CO2 emissions through improved engine efficiency, capacity engines (V6, V8 and V12 engines). Pumping lower weight and lower frictional losses [6,7]. It involves losses are significantly reduced when the engine is a substitution of a naturally-aspirated engine by an operated in the “part-cylinder” mode. Several engine of smaller swept volume. The downsized engine manufacturers have recently incorporated this is typically turbocharged to maintain adequate levels of application into their models. EPA (2008) and IEA torque and power output. The amount by which the (2005) suggest that CO2 reductions associated to these engines are downsized vary depending on the amount systems range from 6-8%. of boost provided by the turbocharger and/or Variable Compression Ratio (VCR) technology supercharger. For example, automotive brochures enables the compression ratio of an engine to be show that a 1.4 litre engine with the application of both automatically adjusted to optimise the efficiency
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